1. Field of the Invention
This invention relates to a sheet-like ceramic substrate from which a large number of tip resistors or the like are to be produced.
2. Description of the Prior Art
When tip resistors are to be produced, first a green sheet is prepared by forming a thin plate from slurry obtained by mixing a binder resin or the like into ceramic powder, and then a plurality of dividing grooves are formed by press work on the green sheet such that they extend perpendicularly to each other, whereafter the green sheet is baked to obtain a ceramic substrate in the form of a rectangular hard ceramic sheet which has primary dividing grooves and secondary dividing grooves engraved on a surface thereof. Here, the primary dividing grooves denote a plurality of grooves which extend in parallel to a pair of opposing sides or edges among the four sides of the rectangular ceramic sheet, and they are provided to facilitate primary dividing operation at a dividing step which will be hereinafter described. Meanwhile, the secondary dividing grooves denote a plurality of grooves which extend in parallel to the other pair of opposing ones of the four edges of the ceramic sheet and hence extend perpendicularly to the primary dividing grooves, and they are provided to facilitate secondary dividing operation at the dividing step.
Referring to FIG. 2, after a sheet-like ceramic substrate 1 is obtained in this manner, surface electrodes 4 are formed by printing on the sheet-like ceramic substrate 1 such that they extend across the dividing grooves 2, and then resistors 5 are formed by printing on the sheet-like ceramic substrate 1 such that each of them connects a pair of such surface electrodes 4 to each other, whereafter trimming is performed. Then, overcoats 6 are formed by printing such that each of the resistors 5 may be covered by one of the overcoats 6.
After then, the sheet-like ceramic substrate 1 is primarily divided along the primary dividing grooves 2 into a plurality of tablet-like elements, and then, side electrodes are formed at divisional end faces of the tablet-like elements by dipping or a like method, whereafter the tablet-like elements are secondarily divided along the secondary dividing grooves 3 and then processed by plating or the like to obtain a large number of single tip resistors.
Conventionally, such a sheet-like ceramic substrate as shown in FIG. 3 is known as such sheet-like ceramic substrate as described above.
Referring to FIG. 3, the sheet-like ceramic substrate 1 is formed from a ceramic sheet 7 having a square shape having two pairs of opposing sides or edges 7a and 7b. A plurality of primary dividing grooves 2 are formed on a face of the ceramic sheet 7 such that they extend in parallel to the opposing sides 7a while a plurality of secondary dividing grooves 3 are formed on the same face of the ceramic sheet 7 such that they extend in parallel to the opposing sides 7b and perpendicularly to the primary dividing grooves 2. While the primary dividing grooves 2 extend at the opposite ends thereof to the opposing sides 7b of the ceramic sheet 7, the secondary dividing grooves 3 are spaced at the opposite ends thereof from the opposing sides 7a of the ceramic sheet 7 so that an undesirable crack of the ceramic sheet 7 may not be caused by an external force upon printing or the like.
However, the conventional sheet-like ceramic substrate 1 described just above is disadvantageous in that, since the dividing grooves 2 and 3 of the ceramic sheet 7 must have a certain depth in order that no trouble may take place upon dividing operation of the ceramic sheet 7, a crack of the ceramic sheet 7 likely takes place along a primary dividing groove 2 when an impact is applied to the ceramic substrate 7 upon transportation or the like.
Thus, such an improved sheet-like ceramic substrate as shown in FIG. 4 has been proposed. Referring to FIG. 4, the sheet-like ceramic substrate 9 is formed from a ceramic sheet 7 which has a pair of slits 8 formed therein in addition to a plurality of primary and secondary dividing grooves 2 and 3 which are spaced from pairs of opposing sides or edges 7b and 7a, respectively. The slits 8 are formed adjacent the opposing sides 7b of the ceramic sheet 7 on the opposite sides of the secondary dividing grooves 3 and extend at the opposite ends thereof to the opposing sides 7a of the ceramic sheet 7. Then, before primary dividing operation, the ceramic sheet 7 is divided along the slits 8. The sheet-like substrate 9, however, is disadvantageous in that the number of steps of operation is increased because dividing operation of the ceramic sheet 7 along the slits 8 is performed as a preparatory step precedent to primary dividing operation, and accordingly, the workability is low.